FIFTY MILLION YEARS AGO, palm trees grew in the Arctic. Alligators lazed on land devoid of ice; rain fell heavily in the warm, thick air; swollen rivers flooded the ocean with freshwater. And a fern called Azolla covered the surface of the Arctic Ocean in a massive blanket the size of Europe. Over the course of about 800,000 years — a blip in the history of the planet — the fern likely pulled trillions of tons of carbon dioxide out of the air and sank to the bottom of the ocean. Eventually the freshwater tropical fern’s glory days in the Arctic came to an end, and Azolla largely disappeared beneath the sea floor.
In July 2004, a group of scientists and oil drillers set out to study the ocean floor on the world’s first (and only) Arctic scientific drilling expedition. The multinational undertaking was run by the Integrated Ocean Drilling Program (now called the International Ocean Discovery Program). Two ships from Russia and Sweden led the way, cracking the thick ice, while the Vidar Viking of Norway brought up the rear, a 1.5-kilometer-long hollow steel pipe — the drill — dangling delicately beneath its hull.
The ships arrived at the Lomonosov Ridge in the North Pole, where the team drilled and collected 428 meters of core from the ocean floor. Nearly all the cores were broken and incomplete. The expedition could easily have been a failure. But by a wild stroke of luck, expedition scientist Henk Brinkhuis says, “exactly the most critical parts of the history of Earth happened to be in these bits and pieces” — specifically, pieces from 49 million years ago, a time when global temperatures were in dramatic decline.
After traveling by helicopter from the Vidar Viking to the Swedish ship Oden, Brinkhuis prepared a small sample of the core for analysis under a microscope. Looking through the lens, he saw hundreds of thousands of remains that looked like “slimy balls with spaghetti strings sticking out”: fossilized Azolla fern.
Again, another stroke of luck. If Brinkhuis hadn’t been the one looking through the microscope, there may have been no discovery. He was the only scientist on the ship who recognized the specimens because Azolla had shown up frequently during his former oil drilling ventures. Jonathan Bujak, an English paleontologist who has worked in the Arctic since 1973, had seen their microscopic fossils in cores for years too. “But I hadn’t attached any significance to it,” he says.
The proliferation of Azolla 50 million years ago is now referred to as the Arctic Azolla event.
The proliferation of Azolla 50 million years ago is now referred to as the Arctic Azolla event. Scientists still aren’t certain what led to the fern’s decline, but by the end of Azolla’s 800,000-year reign, the world had started cooling to the relatively temperate climate we have today. Because high levels of atmospheric carbon dioxide typically lead to global increases in temperature, scientists believe that Azolla’s immense appetite for carbon dioxide contributed to Earth’s cooling. The fern may have cut atmospheric carbon levels by as much as half.
While this part of its fascinating story only recently came to light, the Azolla fern has been entangled with human history for thousands of years. Today, some see it as a pest — a fast-growing invasive weed that blooms like algae. But many see its vast potential to clean up chemical runoff, act as a sustainable fertilizer, or provide a high-protein food source. Some even believe that the fern could contribute to curbing global warming — a natural solution to an unnatural crisis. I’m determined to find out: Does Azolla live up to the claims?
AZOLLA DOESN’T LOOK MUCH like a fern. With leaves only slightly bigger than a grain of sand, a clump of Azolla could easily fit on your thumbnail. It floats on the surfaces of freshwater ponds and lakes, with its roots hanging limply like wispy hairs in a corn husk. Its color ranges from neon green to rusty red. While the quintessential fern has long green fronds and fiddleheads — single leaves coiled up like a roly-poly bug — a patch of Azolla fern looks vaguely like a miniature leaf pile in the middle of a New England autumn.
But as Azolla makes clear, one should never underestimate something for being small: It’s one of the fastest growing plants on Earth, doubling in size every three to ten days in optimal conditions. If humans exhibited the same tendency, an infant would grow to be four times the height of basketball player Shaquille O’Neal in two months.
How does Azolla grow so fast? The fern allied with a cyanobacterium called Anabaena (Nostoc azollae) that resides in small pockets in Azolla’s leaves. The two species help each other out: Anabaena provides Azolla with nitrogen, and Azolla provides Anabaena with sugars. Truly a friend for life, Anabaena has stuck by Azolla’s side for the past 80 million years. The bacterium has even shed genes that it no longer needs since it cohabits with Azolla. Now, according to Kathleen Pryer, a professor of biology at Duke University, “They can’t live without each other.”
Azolla is the only plant in the world with such a loyal companion. When Azolla reproduces, the fern spores are bathed in a solution containing the bacteria. So when the spore relocates and begins to grow, the bacteria accompany the spore, and their relationship continues across generations.